1. Field of the Invention
This invention relates to power input controls for AC induction motors, particularly to an electronic circuit and method for improving power efficiency of an induction motor which provides optimum controlled voltage in accordance with variation of loading on the motor by employing a micro computer.
2. General Description of the Prior Art
An induction motor employs a principle in which electric power is transferred from primary winding to secondary winding by electro-magnetic induction and converted to motive power for moving the motor. It has been widely used in almost all machines with a wide range of power capacity, because it can be used directly without any additional transformer equipment by using AC line voltage installed in a local power utility of every factory, it is easy to operate owing to its simple structure, and also it is cheap.
But due to its rapidly decreasing characteristic of power factor in light loading, it requires improving its power factor in accordance with rate of loading. Accordingly TRIAC's have been employed in prior induction motors to control phase and improve efficiency. This method is shown in U.S. Pat. No. 4,052,648, in which, however, it should be controlled manually according to loading, it generates large vibration torque by input voltage and load current, and it includes higher harmonic components in light loading. Therefore it usually has not been used in precise controlling devices.